1. Field of the Invention
The present invention relates to a coating composition excellent in weatherability and abrasion resistance, and a resin molded article coated with the composition.
2. Prior Art of the Invention
In general, polycarbonate resins are widely used as a transparent resin material due to their excellent impact resistance and transparency. However, polycarbonate resins have defects in that they are poor in abrasion resistance and solvent resistance and that the surface of a molded article produced therefrom is easily scratched and easily corroded with an organic solvent. In order to overcome these defects, there have been proposed a variety of methods in which such a molded article is coated with a thermosetting resin.
In order to improve the properties, abrasion resistance, etc., of transparent resin articles such as molded articles produced from the above polycarbonate resins, well known are resin articles which are coated, as an undercoat layer, with a coating composition comprising an acrylic polymer and further coated, as an overcoat layer, with a coating composition comprising either a silicon compound or a partial hydrolysis product of a silicon compound and a colloidal metal oxide composed mainly of colloidal silica (TOKKAI 59-109528(1984), etc.). And, the undercoat layer of an acrylic polymer often contains an ultraviolet light absorber in order to prevent crack and a decrease in adhesion to another coating layer, which occur due to photo-oxidative deterioration caused on an article surface by ultraviolet light.
However, such resin articles sometimes turn yellow, suffer cracks or have a coating layer peeled off under the influence of ultraviolet light, water, heat, etc., when used for a long period of time. These phenomena are caused for the following reason. When such resin articles are used for a long period of time, the ultraviolet light absorber migrates onto the coating layer surface and dissipates, i.e. it would not remain on the resin article surface, and the ultraviolet light absorption effect is gradually decreased.
Further, when there is employed a method such as an immersion method, a flow-coat method, or the like, in which an overcoating liquid for coating an undercoated resin article with an overcoat layer is repeatedly used, the ultraviolet light absorber contained in the undercoat layer is eluted into the overcoating liquid when brought into contact with the overcoating liquid, and the concentration of the ultraviolet light absorber in the overcoating liquid gradually increases. As a result, the resultant overcoating liquid shows defectiveness in hardness, a decrease in adhesion properties, etc., and the pot life of such an overcoating liquid decreases.